Often in the manufacture of electrical devices and components ultrasonic welding operations are performed to join sections of a given device's casing. Ultrasonic welding is a well known technique for joining materials such as plastic, which are often used as a casing materials. In a typical device, the casing consists of a housing and a cover. The housing comprises a majority of the casing, and has an opening to allow the various components of the device assembly to be placed in the housing. The cover is typically a flat piece that fits over the opening, and has features which engage corresponding structure around the edge of the opening. These structures are commonly referred to as energy directors, and are melted together upon application of ultrasonic vibrations.
To apply the ultrasonic energy, the housing must be rigidly held while an ultrasonic horn pushes the cover against the housing, and then vibrates the cover. The resulting vibrations between the cover and housing produces friction, which in turn heats and melts the parts together. If the pressure applied by the horn is not uniform, when the material melts, it is possible that some of the melted material may be forced out between the two pieces. This ejected material is referred to as flashing, and is normally considered a defect.
Since the pressure exerted by the horn must be uniform to minimize the occurrence of flashing, the nest used to support the housing must be correctly aligned. However, even if the level of the nest is optimized, the errors in housing position due to hand operations still results in occasional flashing defects. Due to the sensitivity of alignment, operators are limited in the speed with which the equipment may operate without excessive defect rates. To increase production volume, a manufacturer must add welding stations to allow enough time for operators to carefully align the assemblies in the nest.
In high volume manufacturing the cost of additional equipment and labor can be prohibitive, and affects the manufacturers ability to bring the product to market at a competitive price. Therefore there exists a need to eliminate defects induced by hand placing parts for ultra-sonic welding operations, and further there exists a need to increase the speed at which ultrasonic welding operations can be commenced.